Q: My local fish store does not have kosher supervision and mostly sells fish with the skin already removed. Is there a problem buying fish from this source?
A: It is forbidden to purchase fish without skin, unless the skin was removed under kosher supervision. This is because once the skin of a fish is removed, it is impossible to identify the particular species. (There is an exception to this rule which will be discussed further on.) Fish labels tend to be meaningless due to the prevalence of species substitution; that is, when one species of fish is sold as another species for the purposes of profit. Sellers will often label low-value species as more expensive ones for the sake of making a greater profit. It is increasingly common, for example, for a non-kosher catfish called basa or tra to be mislabeled as grouper (a kosher species that sells for much more) in order to avoid import duties. In fact, grouper and basa look nothing alike, and one would imagine that consumers would immediately realize that the fish is mislabeled. However, this is not always the case.
Q: Is there anything else aside from skin that I need to check for when purchasing fish in a fish store without kosher supervision?
A: In addition to ensuring the fish has skin, one must check for the presence of scales. For a fish to be considered kosher, the Torah states it must have snapir (fins) and kaskeses (scales). The Gemara, however, states that all fish that have scales have fins (Chullin 66b), so in practice, one only needs to ascertain that the fish has scales in order to be sure that it’s kosher.
It is important to note that while kaskeses is generally translated as scales, not all scales are considered kaskeses. Ramban, in his commentary on the Torah, explains that kaskeses are scales that can be easily removed by hand or with a knife without tearing the skin. Scales that are embedded in a fish or are not visible to the naked eye are not considered kaskeses. The Ramban’s definition is universally accepted.
In 2019, Oceana, a marine conservation nonprofit that studies fish fraud, issued a new report on the state of fish fraud in US. The report found that 20 percent of the 449 fish they tested were incorrectly labeled. In fact, Oceana recommends buying fish with skin on it to avoid buying a fake!
What are examples of fish with scales that are not easily removed and are therefore not kosher? Sturgeon has scales, but its scales are covered with ganoin (an enamel-like substance) and cannot be removed without tearing the skin of the fish. Burbot has cycloid scales, yet because its tiny scales are deeply-embedded in its skin, they cannot be removed without damaging the fish. Sand lances may have tiny scales, but since they are not visible, the fish is not kosher.
Q: I understand there are several different scientific classifications of scales. Which are kaskeses?
A: Though scientists categorize scales by certain characteristics, the Torah is only concerned with whether or not a scale can be easily removed without tearing the skin, irrespective of its shape, color or size. From the Torah’s perspective, the various scientific classifications of scales are irrelevant. Statements made by “experts” about certain types of scales always being kosher are not true.
Q: How does one remove the scales?
A: To check if a fish is kosher, one must ascertain whether or not its scales can be properly removed. On a kosher fish, one end of the fish’s scales is attached to the skin perpendicular to the fish’s head; the other end of the scale, pointing toward the tail, is not attached. To remove the scales, one must grasp the end that is not attached and gently pluck it off from the side of the fish. If removing the scale did not damage the skin, then the fish is kosher.
Q: I heard that some people bring a knife from home to the fish store, because the one used in the store might have residual fat from a non-kosher fish left on the blade. Is this true, and what should I do if I don’t have a knife with me?
A: Yes, there is a concern that a worker in a store without kosher supervision might use the same knives for kosher and non-kosher fish (even when they claim to have a kosher knife only used on kosher fish). You can bring a knife from home to avoid this concern, but there is another option: you can have the store wash the knife thoroughly. Check that the blade is truly clean (and not just rinsed superficially). The board on which the fish is sliced must be properly washed as well, or covered with parchment paper, to protect the kosher order from being compromised by residue left on the board from a previous non-kosher order (you may bring your own cutting board as well). Make certain, as well, that the worker cutting the fish washes his hands or changes his gloves before handling your kosher fish. If the flesh of kosher fish touches non-kosher fish oil, one cannot merely rinse the fish; rather, one must scrub it vigorously (referred to in halachah as shif-shuf gadol) or scrape the point of contact with a knife or stiff-bristled brush (referred to in halachah as graida).
Try to shop during hours when the store is less busy. Fish sellers will be more cooperative and conform to the necessary requirements for a kosher order, as described above, if there are fewer customers waiting.
Q: What about salmon? Is it true that the OU endorses buying salmon without skin and without a hashgachah?
A: According to the OU, the red salmon color is considered an acceptable identifying mark for kosher. As such, the OU permits purchasing skinless salmon without certification.
As long as the consumer is familiar with what salmon looks like, there is no concern that a non-kosher fish will be substituted for salmon. While there are other fish that look very similar to salmon (some types of trout, Arctic char, etc.), they are all kosher
Q: What about the knives used in salmon-processing plants, and how does that differ from knives used in the local (non-certified) fish store?
A: Wild and farmed-salmon factories produce copious amount of fish every day. Even if a non-kosher product ends up intermingled with the kosher fish and is therefore cut with the knives used in these factories, any non-kosher residue on the knife would be eliminated as the first few pieces of fish are cut. The fish with any non-kosher residue would be mixed in with thousands (or tens of thousands) of other salmon, which are perfectly clean of residue, and therefore the former would be considered halachically nullified (batul).
In the case of the local fish store, the seller likely does not cut such large amounts of the same product at one time. One therefore needs to be concerned whether the same knife is used for both kosher and non-kosher (or skinless) fish; both the knife and cutting board present concerns, as explained above. If one does not bring his own knife and board, he may ask the store employee to wash theirs, and confirm that they are clean before he begins slicing the fish, as mentioned above. If one forgot to check the cleanliness of the blade and board, or if one is afraid that they were not cleaned properly, all is not lost! Wash off the fish thoroughly and scrape the surface of the fish with the sharp side of a knife to remove any residue which might remain.
Rabbi Chaim Goldberg, the OU Kosher fish expert, serves as a rabbinic coordinator at OU Kosher. To submit questions for future columns, please e-mail firstname.lastname@example.org or call the Kosher Consumer Hotline at 212-613-8241.